On 2012-03-31 08:31, Tao Ma wrote:> From: Tao Ma <boyu.mt@taobao.com>> > In cfq, when we calculate a time slice for a process(or a cfqq to> be precise), we have to consider the cfq_target_latency so that all the> sync request have an estimated latency(300ms) and it is controlled by> cfq_target_latency. But in some hadoop test, we have found that if> there are many processes doing sequential read(24 for example), the> throughput is bad because every process can only work for about 25ms> and the cfqq is switched. That leads to a higher disk seek. We can> achive the good throughput by setting low_latency=0, but then some> read's latency is too much for the application.> > So this patch makes cfq_target_latency tunable through sysfs so that> we can tune it and find some magic number which is not bad for both> the throughput and the read latency.